Thimerosal–Should I worry about mercury in vaccines for my dog or cat?

Many health concerns among pet owners reflect concerns regarding human health that have been extrapolated to the health of our pets. It is natural to assume, or at least suspect, that factors which influence human health also influence the health of our animal companions. This doesn’t always turn out to be true, but it often does. Given there is much more information and scientific evidence about health risk factors available in the human health field than in veterinary medicine, sometimes it makes sense to apply this information to health issues in our pets, though

We must always bear in mind the dangers of extrapolation between species with significant biological differences.

Concerns about the safety of vaccinations for children have been partly responsible for stimulating increased concern about the safety of veterinary vaccines. I have addressed this subject several times (e.g. 1, 2), but recently I was asked by another practitioner about a very specific vaccine safety issue—the risks, if any, of thimerosal.

Thimerosal is a preservative used in vaccines since the 1930s. Such preservatives which added to vaccines following several terrible incidents of children acquiring deadly infections from contaminated vaccines. It has been widely used since, and few health concerns have been raised until quite recently.

Following some of the first allegations that vaccines, in particular the MMR vaccine, might be associated with an increased risk of autism or other developmental disorders, the hypothesis was put forward that thimerosal might be responsible because it is a mercury compound, and other types of mercury compounds are known to have toxic effects on the nervous system.

Because of public concern about this, thimerosal was removed from most vaccines for children in the U.S. in 1999 pending additional research, a recommendation endorsed by the American Academy of Pediatrics. Subsequently, additional research and epidemiologic evidence following the removal of thimerosal from vaccines concluded quite definitively that there was no evidence of any increase in risk associated with this compound. The AAP withdrew their statement on removing thimerosal from vaccines in 2002 based on new evidence.

Thimerosal is present in some veterinary vaccines. I have not found any specific published research on the issue of whether this preservative has harmful effects when used as a preservative in vaccines for dogs or cats, apart from one study suggesting it can cause local irritation that might confuse the results of one kind of allergy test. The only study regarding thimerosal in vaccines looked at whether the thimerosal in vaccines influenced the mercury content of hair in dogs. This study found that thimerosal in vaccines did not increase the amount of mercury detected in the dogs’ hair, and that this mercury was primarily associated with eating foods containing fish.

I am not aware of any scientific evidence showing any significant health risks associated with thimerosal in veterinary vaccines. According to one toxicologist I contacted, there are no clinical studies in veterinary patients, but studies in laboratory animal research suggests no risks at the levels used in vaccines. This is consistent with the robust evidence in humans that thimerosal used in vaccines is not a health risk.

This has not stopped the more extreme voices in the anti-vaccine community from insinuating that thimerosal is a health risk for our pets despite the lack of evidence for this. There is at least one veterinary vaccine marketed as “thimerosal free,” and there is no harm in using such a vaccine. But there is also no reason to think this vaccine is any safer than those which do contain thimerosal, and there is no reason to expect your veterinarian to prefer it over other brands.

27 Responses to Thimerosal–Should I worry about mercury in vaccines for my dog or cat?

Paragraph 4 seems to imply that MMR vaccines contain Thimerosal; they do not.

Headlines about a 2005 NIEHS primate study by Burbacher et al. announced that mercury left the blood quickly, sidestepping the more ominous implication — because the mercury quickly lodged in the animals’ brain tissue.

Questioning the sensibility of injecting any form or amount of neurotoxic mercury into animals or humans does not make one “anti-vaccine.” Rather, such questioning indicates one’s willingness to reexamine all scientific beliefs, no matter how dearly held or whomever profits, should new information become available that renders status quo less certain.

You are correct that MMR used to contain thimerosal. It was removed due to public concern, and it has not been put back. Some other vaccines do still contain thimerosal. The important point was that the evidence clearly shows no harm was done by thimerosal when it was in the MMR vaccine, and that since it has been removed there has been no decline in the diseases that were claimed to be caused by thimerosal.

Questioning the sensibility of injecting any form or amount of neurotoxic mercury into animals or humans does not make one “anti-vaccine.”

The problem here is with your use of the word “neurotoxic,” which implies that thimerosal invaccines is the cause of neurologic disease. This turns out not to be true. Thimerosal can, of course, be toxic at sufficient doses, but then so can water. It is not toxic at the dose present in vaccines. And mercury can be neurotoxic, but ethyl mercury and methyl mercury are different compounds, and a large part of the unnecessary fear of thimerosal stems from not understanding the biologically relevant difference.

It was, at one time, perfectly reasonable to ask whether thimerosal in vaccines was safe, which is why the AAP recommended its removal from vaccines. It is now clearly demonstrated that it is safe, which is why that recommendation was later withdrawn. Continuing to claim that thimerosal in vaccines is unsafe is, then, a pretty reliable indicator of an anti-vaccine agenda since the question has already been answered from a scientific point of view.

It is important to understand the effect of the precise molecule rather than any given element, after all we need salt, but ingesting either sodium or chlorine in their elemental forms would be harmful; assuming you could get either past your mouth and into your digestive system. And there are plenty of examples of more complex molecules where one form is biologically essential whereas it’s mirror image is damaging or even lethal.

The thimerosal free rabies vaccine comes in 1 year and 3 year, so if I know the dog has to get it again in 1 year, then every 3 years, can he get the 1 year for the first shot?

IMRAB 3 is recommended for the vaccination of healthy cats, dogs, ferrets, horses, cattle and sheep against disease caused by rabies virus. Three-year duration of immunity in dogs, cats and sheep
One-year duration of immunity in horses, cattle and ferrets

IMRAB 1
IMRAB 1 is recommended for the vaccination of healthy dogs and cats against disease caused by rabies virus. One-year duration of immunity in dogs and cats

Okay, I spoke to my vet today, he told me the thimerosal free rabies vaccine was really more beneficial for cats, due to that injection site sarcoma they sometimes get.
He said it wouldn’t make a difference for dogs.

I’m afraid your vet is giving you merely his opinion, and it is not an opinion based on scientific evidence. It is true that cats are apparently more prone to vaccine-associated sarcomas than dogs, though the incidence is still very low (1 out of every 5,000-10,000 vaccinations). However, there is no evidence at all that thimerosal has anything to do with this. There was some evidence that aluminum adjuvant might have been associated with the occurrence of these sarcomas, and most of us now use adjuvant-free vaccines such as the Merial Purevax, but even this hypothesis is tentative, and it is not yet entirely clear if the change in vaccine type will have any effect on the rate of occurrence of these tumors. So again, there is no reason to think a thimerosal-free vaccine is any safer than any other vaccine.

Skeptvet,
The MMR never had thimerosal: the mercury would have killed the live viruses in the vaccine. The MMR is dangerous for other reasons, the live viruses are dangerous, and the vaccine often causes vaccine encephalitis and many types of subsequent damage. The killed virus vaccines used to contain mercury as a preservative, and still have dangerous levels of “trace” amounts.

As for the mercury issue, there is no evidence it was ever a health risk in any vaccine, there have been not reductions is potential health problems since it was removed from routine childhood vaccines, and you need to provide actual evidence that any “trace” amounts present a health risk.

As for encephalitis, “often causes” is a lie. Per the FDA, which is a far more reliable source than you are:

Encephalitis has been reported approximately once for every 3 million doses of MMR vaccine. Post-marketing surveillance of more than 400 million doses distributed worldwide (1978 to 2003) indicates that encephalitis is rarely reported after MMR vaccination. In no case has it been shown conclusively that encephalitis was caused by a vaccine virus infection of the central nervous system.”

Vaccines can cause encephalitic brain damage just from the reaction of the immune system to the perceived danger of the vaccine suddenly showing up in the blood, having bypassed the body’s filtering system. However, mercury in vaccines can cause vaccine encephalitis all by itself, and several generations of children have been disabled by it. I reacted to the mercury in a tetanus booster many years ago by having both arms paralyzed the same day, and was later diagnosed by MRI with multiple sclerosis, all the symptoms of which are identical to those of mercury poisoning. My newborn reacted to the mercury in the hep-B vaccine given at birth without permission, with vaccine encephalitis and was later diagnosed with autism. A mercury-containing flu vaccine paralyzed my father for the last three years of his life. Some people have a genetic inability to excrete the vaccine mercury as quickly as others do, and in us it is stored in the brain, bones, or internal organs for life, and a fever can pull it out of the bones and set off new symptoms.

The books The Age of Autism and Evidence of Harm show how mercury in vaccines causes autism and many other severe conditions, with many scientific and epidemiological studies cited. Books by the holistic veterinarians Dr. Richard Pitcairn, Dr. Marty Goldstein, and Dr. Don Hamilton give the scientific evidence and many examples from their practices, that mercury and aluminum (etc.) in pet vaccines, as well as in human, often cause serious and even deadly autoimmune disease and cancer.

Again, you make lots of claims here without any evidence to back them up. They are claims that are contradicted by actual scientific evidence. You do your cause no good by them citing the likes of Richard Pitcairn, whose faith in the religion of homeopathy eliminates any credibility and who himself presents no scientific evidence to support claims about vaccine but only his wildly implausible opinions and biased anecdotes. The purported link between vaccines and autism has been conclusively disproven and rejected by every legitimate scientific and public health organization and mainstream autism research and advocacy groups. There simply is no truth to the claims you make, and without real evidence to support them there is no reason for anyone to accept them.

Thank you, Cia Parker. Anecedotal evidence is too swiftly rejected by medical and scientific communities heavily dependent on pharmaceutical revenues and attentions. Besides anecdotal evidence which puts the CDC’s one-in-a-million claim to shame, there are plenty of doctors and scientists, with legitimate credentials and research to back them up, who are raising warning flags about vaccine safety. We would do well to power past the cognitive dissonance gut-reaction and learn truth.

It’s interesting because you ask for evidence and when I attempted to post this comment with links to all these doctors’ videos on YouTube, your site said my comment looked “spammy” and to try again. You want evidence, but don’t allow it? Odd. Anyway, I came here searching for information about pet vaccinations after seeing a recent news story about dogs, vaccinations, and autoimmune disorders (let’s see if your page will let me link it…nope, no luck, took this one out first). I was disappointed to find your site so quick to adopt the industry line of “vaccines are safe and effective, vaccines don’t cause autism, vaccines don’t contain thimerosal, everything’s fine, folks, just move along.”

Science is not a popularity contest, and lists of doctors who believe something isn’t evidence, merely opinion. Of course, even with this sort of illegitimate form of argument, you would lose since the overwhelming majority of doctors do support vaccination. All of the links you provide are to misinformation and propaganda that have been rebutted a million times. The problem, of course, is that anti-vaccine activists aren’t interested in facts and evidence since this is an emotion-driven movement supported by fear and mistrust, not science:

Just so you know, Liz, wordpress injects “looks like spam” whenever ANYONE posts more than one link – it has to get through the wordpress filters. But I digress, you probably just think skeptvet censored you. Likewise, it’s his blog and it’s been made clear several times that link spam and propaganda site links will not be tolerated.

You don’t have a valid argument, least of all one supported by real science and research. Take some time to read the links skeptvet offered you – you’ll find out how valid research is done.

What do you think about Benadryl 1 hour prior and a shot of prednisone as a prophylactic at the same time as the rabies vaccine in an adult dog with unclear vaccination history?
And a rabies titer 1 year later prior to the booster? If the titer was high or adequate wouldn’t that indicate the booster wasn’t indicated?

The intention of premedication is to prevent acute hypersensitivity reactions. Unfortunately, they don’t actually prevent such reactions. The benadryl may suppress some of the symptoms, such as hives, but the reaction still occurs. The prednisone works through a mechanism involving protein production, so it doesn’t take affect for 4-6 hours, so premedication right before a vaccine isn’t going to be useful. And in any case, such treatment isn’t indicated in dogs that don’t have a history of such hypersensitivity reactions, and the vast majority of dogs do not have these reactions.

As for titers, these can be useful to prove that a dog has had an appropriate protective response to vaccination. However, they don’t tell us if a dog needs to be revaccinated. A positive titer indicates protection, but a negative titer does not indicate susceptibility since there are other elements of the immune system the titer does not measure which are important in immunity. And a titer will not substitute for legal rabies vaccination requirements, so dogs who have not had the rabies vaccine as required by law will be considered unvaccinated regardless of their titers.

Thank you. Maybe I will give the Benadryl prior to the appointment and hang out in the waiting room for an hour afterwards. I might skip the prednisone, I figured it would only prevent an acute reaction anyway, I will give it some more thought.

“And a titer will not substitute for legal rabies vaccination requirements, so dogs who have not had the rabies vaccine as required by law will be considered unvaccinated regardless of their titers”.

I know that, my concern would be that if the dog has a high or adequate rabies titer would giving him the booster overload his immune system and possibly cause adverse effects. I understand that “the law is the law”. However…..

While that’s perfectly sound logic, the problem is that the issue of “overloading: the immune system isn’t a real one. Our immune system is exposed to more antigens through normal living (eating, contact with other people, paper cuts, and so on) in about 3 weeks than in the entire childhood vaccination series (see here). The immune system competently handles far more challenges every day than it experiences through vaccination. An appropriate titer does indicate protection against rabies, and hopefully the law will eventually be changed to allow use of this measure. But either way, there is no reason to be concerned about vaccinating even if the dog has an adequate titer.

Quoted from skeptvet: “Thimerosal can, of course, be toxic at sufficient doses, but then so can water.” I am sorry (chuckle) but that made me lol when I read it. Thimerosal is mercury, mercury is toxic at any concentration and in any of its forms (it undergoes conversion within our bodies – just like it does in fish!). You present a very one-sided story here – read all of the reports – not just the ones that support your views. Readers, be warned – and do your own research. Read the book, Mercury-free by James Hardy to begin to learn about how we are poisoning ourselves and our environment with mercury. And, to be sure, there is a connection between Autism and mercury vaccines. For example, read ‘Blood Levels of Mercury Are Related to Diagnosis of Autism: A Reanalysis of an Important Data Set’ M. Catherine DeSoto, PhD, and Robert T. Hitlan, PhD, Journal of Child Neurology, a highly cited article refuting the original study’s claim (analyses were conducted incorrectly).

The cdc is currently under investigation for ordering their scientists to cover us evidence of a link between mmr and autism after senior research scientist and whistleblower William Thompson revealed their activities. Remember in the 50’s how we were told by “every reputable agency” that Tabasco doesn’t cause cancer? Yeah…
A list of studies that show a link between vaccines and health issues-

The claim that the CDC has covered up evidence regarding vaccines and autism is a bogus internet conspiracy that has been debunked numerous times (1, 2). Similarly, the evidence that vaccines are not associated with autism is overwhelming, and not a single reputable scienctific, public health, or autism advocacy group accepts this lie. You are living in a fantasy world.